In most cases, semiconductor chips are incorporated into an individual protective package, connected onto a printed circuit board. In a conventional semiconductor apparatus, external terminals (connection terminals) extending from the protective package are bonded onto a flat plane of the printed circuit board. For example, in a flat package, leads (connection terminals) are bonded around the package onto the surface of the printed circuit board. The pitch (spacing) between two adjacent leads is designed to be small, such as 1.27 mm, so as to contribute to increasing the number of leads (terminals). Such a package is designed small in size and is shaped almost square, so that connecting lines (inner leads) in the package can be designed to have the same length; and therefore, it is easy to control impedance thereof Such package design is useful for a high performance semiconductor apparatus.
According to the conventional semiconductor apparatus, the connection terminals are connected onto the single plane of the printed circuit board, so that it is required to narrow the pitch between two adjacent terminals in order to increase the number of terminals. The pitch of the connection terminals is basically defined by the mounting technique, for example, 0.3 mm of pitch would be the minimum for QFP in reflow solder-bonding technique. Accordingly, in order to increase the number of the connection terminals, the only way is to make a pitch of terminals narrower than 0.3 mm. According to the current mounting technology, however, it is difficult to mount the semiconductor apparatus, having the connection terminals with a pitch of less than 0.3 mm, onto the printed circuit board.